Immunogenicity of Mycobacterium avium subsp. paratuberculosis proteins in Crohn's disease patients

The association between Mycobacterium avium subsp. paratuberculosis (MAP) and Crohn's disease (CD) is supported by several studies reporting the detection or isolation of MAP from human tissues, but a direct association is still debatable. Objective. To evaluate the survival of MAP in human intestinal cells and to measure the presence of antibodies against two mycobacterial proteins necessary for the survival of the bacterium in the sera of CD patients. Material and methods. Human-derived intestinal cells were infected with three isolates of MAP and the survival of the microorganism was determined. The presence of antibodies against protein tyrosine phosphatase A (PtpA) and protein kinase G (two proteins secreted within the host in the early stages of the invasion) in the sera of CD patients was evaluated. Sera of 20 CD patients and 20 controls were collected and the presence of the antibodies was assayed using enzyme-linked immunosorbent assay (ELISA). Secretion of the PtpA in vivo was visualized by immunostaining. Results. MAP survived in intestinal cells, and immunostaining of PtpA showed that the protein was secreted within these cells. Wilcoxon rank sum test revealed that CD patient sera had significantly higher titer of antibodies specific for both of these antigens compared to controls. ELISA results for either protein were not statistically different between men and women. Conclusions. The presence of specific antibodies against mycobacterial proteins essential for establishing an infection in the host suggests that MAP can potentially be active in CD patients, and a serological test can be developed for early detection of MAP in CD patients.